1. Field:
The field of the invention is methods for recovery of hydrogen and sulfur by breakdown of gaseous hydrogen sulfide (H.sub.2 S)
2. State of the Art:
Over a period of several decades, many chemical process workers have studied methods for the decomposition of hydrogen sulfide to yield hydrogen and elemental sulfur. The reason for these efforts has been the very large quantities of hydrogen and elemental sulfur contained in the noxious hydrogen sulfide, H.sub.2 S, produced in the refining of petroleum and the purifying of natural gas. At present, H.sub.2 S is partially oxidized to produce sulfur dioxide (SO.sub.2), which reacts with residual H.sub.2 S to form elemental sulfur and water. This method is known as the Claus process. Kalina and Maas.sup.5 noted that, in 1982, conversion of hydrogen sulfide by this method yielded 4.2.times.10.sup.6 long tons of sulfur, approximately 50% of the sulfur produced in the United States that year. Also noted was the fact that recovery of the stoichiometric amount of hydrogen associated with this sulfur could, if recovered, provide a very significant portion of the hydrogen required for heavy crude oil upgrading, and for coal liquefying and gasifying.
The following H.sub.2 S decomposition methods have been studied and described in recent papers:
direct, high temperature thermal decomposition, with separation of the resultant gases by means of pressure swing absorption of H.sub.2 S.sup.1 ; PA1 direct high temperature thermal decomposition, with high temperature separation of gases by means of porous ceramic membranes.sup.6 ; PA1 thermochemical cycles involving the reaction of H.sub.2 S with a metal or metal sulfide to form a higher sulfide and evolve hydrogen, followed by thermal decomposition of the higher sulfide.sup.8 ; PA1 electrochemical processes for H.sub.2 S decomposition.sup.4,5 ; and PA1 photolytic decomposition of H.sub.2 S via the irradiation of semiconductor electrodes or treated particles with light.sup.2.
All of these methods, with the possible exception of the photon based processes, appear to offer possibilities for development of practical approaches for recovery of both S.sub.2 and H.sub.2. However, none have been developed sufficiently nor widely adopted by the petroleum industry, which remains in need of a practical, economical method.